M.A.
Hi A.
Your safest bet would be to contact the mom's of the boys with the allergies. This will accomplish two things. You will know for sure what they can eat, and the mom's will feel that their children's allergies are being taken seriously.
I used to nanny for a child with many life threatening food allergies and he rarely was invited anywhere due to no-one wanting to ask what he could eat. He ate very healthily. A lot of fresh food, fruits, veggies and a lot of meat. He had to be careful of meat though as he was also allergic to hormones in some meats! Yeah, he was a tricky kid to feed but he was a great kid.
Well done to you for wanting them to feel as though they are normal and will be safe at your son's party.